KR20240097028A - Electrolyte solution for lithium secondary battery and Lithium secondary battery comprising the same - Google Patents

Abstract

The present invention relates to an electrolyte solution for a lithium secondary battery that can improve the flame retardancy characteristics as well as the lifespan characteristics and output characteristics of a high-capacity lithium secondary battery, and to a lithium secondary battery containing the same. It relates to a lithium secondary battery.
An electrolyte solution for a lithium secondary battery according to an embodiment of the present invention includes lithium salt; a first solvent consisting of a fluorinated ether-based solvent having lithium salt non-dissociation properties; It includes a second solvent consisting of an ether-based solvent having lithium salt dissociation properties.

Description

Electrolyte solution for lithium secondary battery and lithium secondary battery comprising the same {Electrolyte solution for lithium secondary battery and Lithium secondary battery comprising the same}

The present invention relates to an electrolyte for lithium secondary batteries and a lithium secondary battery containing the same, and more specifically, to an electrolyte for lithium secondary batteries that can improve flame retardancy characteristics as well as life characteristics and output characteristics of high-capacity lithium secondary batteries, and lithium containing the same. It's about secondary batteries. It's about lithium secondary batteries.

A lithium secondary battery is an energy storage device consisting of a positive electrode that provides lithium when charging, a negative electrode that accepts lithium, an electrolyte that is a lithium ion transfer medium, and a separator that separates the positive and negative electrodes. Lithium ions intercalate at the positive and negative electrodes. Electrical energy is generated and stored by changes in chemical potential during intercalation/deintercalation.

These lithium secondary batteries were mainly used in portable electronic devices, but recently, with the commercialization of electric vehicles (EV) and hybrid electric vehicles (HEV), lithium secondary batteries have also been used as an energy storage method for electric vehicles and hybrid electric vehicles. is being used.

Meanwhile, the performance of lithium secondary batteries is determined by the characteristics of the four core materials: anode, cathode, separator, and electrolyte.

In particular, in order to accelerate the commercialization of electric vehicles, which are eco-friendly vehicles, it is essential to improve energy density at the cell level to improve driving range, and low-cost, fast charging and rapid discharging technology, and high safety technology are also essential.

In addition, the importance of low-viscosity solvents and additives included in the electrolyte of lithium secondary batteries is being emphasized to improve battery performance and stability related to output.

Meanwhile, electrolytes are formed by dissociating lithium salts and various functional additives in organic solvents. In this case, carbonate-based organic solvents, ester-based organic solvents, and ether-based organic solvents are used alone or in combination as organic solvents.

However, carbonate-based organic solvents are flammable organic substances, and there is a risk that battery safety may be compromised due to side reactions with lithium metal (lithium salt) and the formation of dendrites.

In addition, carbonate-based organic solvents have a low flash point and high volatility, so when used at high temperatures, they cause a combustion reaction with electrode materials, rapidly increasing the battery temperature, and ultimately causing thermal runaway.

Therefore, the development of a stable electrolyte can be said to be a key factor in improving the energy density of lithium secondary batteries. In particular, there is a need to develop mid- to large-sized lithium secondary batteries for electric vehicles or hybrid vehicles that can be used in various temperature environments while ensuring excellent output/lifespan characteristics.

The content described as background technology above is only for understanding the background to the present invention, and should not be taken as an admission that it corresponds to prior art already known to those skilled in the art.

Public Patent Publication No. 10-2007-0001196 (2007.01.03)

The present invention relates to an electrolyte solution for a lithium secondary battery that can improve the flame retardancy characteristics as well as the lifespan characteristics and output characteristics of a high-capacity lithium secondary battery, and to a lithium secondary battery containing the same. It provides a lithium secondary battery.

The technical problems to be achieved by the present invention are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those skilled in the art from the description of the present invention. You will have to see it.

An electrolyte solution for a lithium secondary battery according to an embodiment of the present invention includes lithium salt; a first solvent consisting of a fluorinated ether-based solvent having lithium salt non-dissociation properties; and a second solvent consisting of an ether-based solvent having lithium salt dissociation properties.

The first solvent is characterized in that it contains a fluorinated ether-based solvent, which is 1-methoxyheptafluoropropane, represented by [Formula 1] below.

… … … [Equation 1]

The second solvent is characterized in that it contains dimethyl ether (DME).

The mixing ratio of the first solvent and the second solvent is characterized in that the first solvent is mixed in a weight ratio of 50% or more.

The mixing ratio of the first solvent and the second solvent is preferably 10:90 to 80:20 in weight ratio.

An electrolyte solution for a lithium secondary battery, characterized in that the concentration of the lithium salt is 0.1 to 3.0 mol.

The lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , LiB(C ₂ O ₄ ) ₂ , LiPO ₂ F ₂ , Li(SO ₂ F) ₂ N, LiFSI, or (CF ₃ SO ₂ ) ₂ NLi. It is characterized by one or a mixture of two or more types selected from the group consisting of.

Meanwhile, a lithium secondary battery according to an embodiment of the present invention includes the above-described electrolyte solution. And, a positive electrode containing a positive electrode active material made of Ni, Co, and Mn; A negative electrode containing one or two or more types of negative electrode active materials selected from carbon (C)-based or silicon (Si)-based; It further includes a separator interposed between the anode and the cathode.

According to an embodiment of the present invention, the effect of improving the flame retardancy of a lithium secondary battery can be expected by mixing 50% or more of a fluorinated ether-based solvent with excellent flame retardant properties among the solvents forming the electrolyte solution.

In addition, according to embodiments of the present invention, the effect of increasing the lifespan of a lithium secondary battery and improving battery output characteristics can be expected.

Figure 1 is a diagram showing the surface condition after flame testing of various samples according to changes in the type of solvent.
Figure 2 is a diagram showing the dissociation characteristics of lithium salt according to changes in the type of solvent;
Figure 3 is a graph showing the results of an experiment evaluating the discharge capacity and life capacity maintenance rate of Examples and Comparative Examples according to changes in the type of solvent;
Figure 4 is a graph showing the results of an experiment evaluating the output performance of Examples and Comparative Examples according to changes in the type of solvent.

Hereinafter, embodiments disclosed in the present specification will be described in detail with reference to the attached drawings. However, identical or similar components will be assigned the same reference numbers regardless of reference numerals, and duplicate descriptions thereof will be omitted.

In describing the embodiments disclosed in this specification, if it is determined that detailed descriptions of related known technologies may obscure the gist of the embodiments disclosed in this specification, the detailed descriptions will be omitted. In addition, the attached drawings are only for easy understanding of the embodiments disclosed in this specification, and the technical idea disclosed in this specification is not limited by the attached drawings, and all changes included in the spirit and technical scope of the present invention are not limited. , should be understood to include equivalents or substitutes.

Terms containing ordinal numbers, such as first, second, etc., may be used to describe various components, but the components are not limited by the terms. The above terms are used only for the purpose of distinguishing one component from another.

Singular expressions include plural expressions unless the context clearly dictates otherwise.

In this specification, terms such as “comprise” or “have” are intended to designate the presence of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification, but are not intended to indicate the presence of one or more other features. It should be understood that this does not exclude in advance the possibility of the existence or addition of elements, numbers, steps, operations, components, parts, or combinations thereof.

The electrolyte solution for a lithium secondary battery according to an embodiment of the present invention is a material that forms an electrolyte applied to a lithium secondary battery and consists of a lithium salt and a solvent.

Lithium salts are LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , LiB(C ₂ O ₄ ) ₂ , It may be one or a mixture of two or more selected from the group consisting of LiPO ₂ F ₂ , Li(SO ₂ F) ₂ N, LiFSI, or (CF ₃ SO ₂ ) ₂ NLi.

At this time, the lithium salt may be present in the electrolyte solution at a total concentration of 0.1 to 3.0 mol, preferably 1.0 to 2.0 mol. More preferably, it is present at a concentration of 2.0 mol.

In order to provide flame retardant properties to the electrolyte solution, the solvent is used by mixing a first solvent with flame retardant properties and a second solvent with dissociation properties of lithium salt.

At this time, the first solvent may be one type or a mixture of two or more types selected from the group consisting of fluorinated ether-based solvents with flame retardant properties.

For example, 1-methoxyheptafluoropropane (hereinafter referred to as “MPFPE”) represented by [Formula 1] can be used as a fluorinated ether solvent.

… … … [Equation 1]

At this time, 1-methoxyheptafluoropropane (MPFPE) used as the first solvent has excellent flame retardant properties and can improve lifespan and output characteristics when used as a solvent in a high concentration salt electrolyte solution.

Therefore, as the first solvent, 1-methoxyheptafluoropropane (MPFPE) can be used alone or a mixture of 1-methoxyheptafluoropropane (MPFPE) and a solvent belonging to the fluorinated ether solvent group.

However, 1-methoxyheptafluoropropane (MPFPE) used as the first solvent is a non-dissociating fluorinated ether-based solvent in which lithium salts do not dissociate. In order to dissociate the lithium salts constituting the electrolyte, a second solvent having lithium salt dissociation properties is used as the first solvent. It is mixed with a solvent to form a solvent.

At this time, an ether-based solvent having lithium salt dissociation properties can be used as the second solvent.

For example, dimethyl ether (DME) can be used as an ether-based solvent used as a second solvent.

At this time, dimethyl ether (DME), used as the second solvent, can dissociate the lithium salt by complementing the lithium salt non-dissociation property of 1-methoxyheptafluoropropane (MPFPE), used as the first solvent.

However, dimethyl ether (DME), which is used as the second solvent, may cause the phenomenon of dissociated lithium ions being electrodeposited on the surface of the cathode. In this case, this reaction is prevented by 1-methoxyheptafluoropropane (MPFPE), which is used as the first solvent. It can be suppressed.

In this way, it is desirable to limit the mixing ratio of the first solvent and the second solvent in order to compensate for each other's shortcomings and maintain their respective strengths, such as flame retardant properties and lithium salt dissociation properties.

For example, it is desirable to mix the first solvent and the second solvent so that the first solvent accounts for 50% or more by weight. More preferably, the mixing ratio of the first solvent and the second solvent is maintained at a weight ratio of 10:90 to 80:20.

If the mixing amount of the first solvent is less than 10%, a problem may occur in which the flame retardant properties of 1-methoxyheptafluoropropane (MPFPE) used as the first solvent are not realized at the desired level, and the mixing amount of the first solvent is 80%. In cases exceeding %, the lithium salt forming the electrolyte solution is not sufficiently dissociated in the solvent due to the lithium salt non-dissociation characteristic of 1-methoxyheptafluoropropane (MPFPE) used as the first solvent, which reduces the capacity and output characteristics of the lithium secondary battery. Problems may arise. Additionally, when the mixing amount of the first solvent is greater than 80%, there is a problem that phase separation of the electrolyte solution occurs.

Meanwhile, the electrolyte solution for a lithium secondary battery according to an embodiment of the present invention may further contain functional additives that perform various functions along with lithium salt, the first solvent, and the second solvent.

For example, various types of cathode film additives that play the role of forming a protective film on the cathode can be used as functional additives. For example, Vinylene Carbonate (hereinafter referred to as “VC”) can be used as a cathode coating additive.

Meanwhile, a lithium secondary battery according to an embodiment of the present invention consists of a positive electrode, a negative electrode, and a separator along with the above-described electrolyte solution.

The positive electrode is made of NCM-based positive electrode active material consisting of Ni, Co, and Mn. In particular, in this embodiment, the positive electrode active material included in the positive electrode is preferably composed only of NCM-based positive electrode active material containing 60 wt% or more of Ni.

And, the negative electrode includes one or two or more types of negative electrode active materials selected from carbon (C)-based or silicon (Si)-based.

The carbon (C)-based negative electrode active material may be at least one material selected from the group consisting of artificial graphite, natural graphite, graphitized carbon fiber, graphitized mesocarbon microbeads, fullerene, and amorphous carbon.

And, the silicon (Si)-based negative electrode active material includes silicon oxide, silicon particles, and silicon alloy particles.

Meanwhile, the positive and negative electrodes are manufactured by mixing each active material with a conductive material, binder, and solvent to prepare an electrode slurry, and then directly coating and drying the electrode slurry on a current collector. At this time, aluminum (Al) may be used as the current collector, but is not limited thereto. Since this electrode manufacturing method is widely known in the field, detailed description will be omitted in this specification.

The binder plays a role in adhering each active material particle to each other or to the current collector. For example, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, and carboxylic acid. Silized polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrenebutadiene rubber, acrylate. Teed styrenebutadiene rubber, epoxy resin, nylon, etc. can be used, but are not limited thereto.

In addition, the conductive material is used to provide conductivity to the electrode, and in the battery being constructed, any electronically conductive material can be used as long as it does not cause chemical change. Examples include natural graphite, artificial graphite, carbon black, acetylene black, Metal powders such as Ketjen black, carbon fiber, copper, nickel, aluminum, and silver, and metal fibers can be used. Additionally, conductive materials such as polyphenylene derivatives can be used one type or a mixture of one or more types.

The separator prevents short circuit between the anode and cathode and provides a passage for lithium ions. These separators are known ones such as polyolefin-based polymer membranes such as polypropylene, polyethylene, polyethylene/polypropylene, polyethylene/polypropylene/polyethylene, polypropylene/polyethylene/polypropylene, or multilayers thereof, microporous films, woven fabrics, and non-woven fabrics. can be used Additionally, a porous polyolefin film coated with a highly stable resin may be used.

Hereinafter, the present invention will be described through examples and comparative examples.

<Experiment 1> Flame retardancy-related experiments depending on the type of solvent

After the flame retardancy test for various types of solvents used as solvents for electrolyte solutions, the damage to the solvent-impregnated separator was evaluated, and the surface condition and flame retardancy were evaluated after the flame test of the solvent-impregnated separator. The results are shown in Table 1 and Figures below. It is shown in 1.

Figure 1 is a diagram showing the surface condition after a flame test of various samples according to changes in the type of solvent.

At this time, in order to simulate the electrolyte solution, 1.0M LiTFSI as a lithium salt was added to the solvent shown in Table 1, and the electrolyte solution thus prepared was sufficiently impregnated into polypropylene material used as a separator in a typical lithium secondary battery, and then a flame retardancy test was conducted. .

In addition, the degree of damage to the impregnated separator was qualitatively evaluated by the relative degree of damage observed with the naked eye for the four types of specimens evaluated. The flame retardancy test was determined based on the UL 94 test standard, and first burn and second burn were respectively The unit of time for extinguishing after burning with a flame for 10 seconds is seconds (sec) and expressed as sec/g.

division lithium salt menstruum Damage to impregnated separator Flame retardancy (sec/g) No. One 1.0M LiTFSI EC:EMC=50%:50% go 78 No. 2 1.0M LiTFSI DME 100% middle 73 No. 3 1.0M LiTFSI PC 100% I 59 No. 4 1.0M LiTFSI 100% MPFPE no damage 15

As can be seen in Table 1 and Figure 1, after the flame test, No. Separation membrane according to 4 Separation membrane according to No. 1 to No. Compared to 3, it was confirmed that there was relatively little damage to the separator.

Also, in terms of flame retardancy, it ranks No. 1. Separation membrane according to 4 Separation membrane according to No. 1 to No. It was confirmed that the flame retardancy was relatively excellent compared to 3.

Therefore, it was confirmed that MPFPE can be used as a solvent to improve flame retardancy.

<Experiment 2> Lithium salt dissociation characteristics experiment according to the type of solvent

In order to complement the lithium salt non-dissociation property of MPFPE, various solvents with lithium salt dissociation properties were mixed 1:1 with MPFPE, and then it was confirmed whether the lithium salt could be dissociated.

At this time, the type of solvent (second solvent) mixed with MPFPE (first solvent) and the experimental results are shown in Table 2 and Figure 2 below.

Figure 2 is a diagram showing the dissociation characteristics of lithium salt according to changes in the type of solvent.

division lithium salt menstruum result No. 5 LiTFSI MPFPE sole Lithium salt cannot be dissociated No. 6 LiTFSI MPFPE+DME Lithium salt can dissociate No. 7 LiTFSI MPFPE+PC Non-uniformity due to solvent phase separation

As can be seen in Table 2 and Figure 2, No. 2 used only MPFPE as a solvent. In case 5, it was confirmed that the lithium salt did not dissociate in the solvent.

On the other hand, No. 1 used a mixture of MPFPE and DME as a solvent. In case 6, it was confirmed that the lithium salt was dissociated in the solvent.

In addition, No. 1 used a mixture of MPFPE and PC as a solvent. In case 7, it was confirmed that although the lithium salt was dissociated in the solvent, it was difficult to use it as a solvent as phase separation occurred between MPFPE and PC used as solvents.

Therefore, in order to sufficiently dissociate the lithium salt while improving flame retardancy, it is possible to use a solvent that is a mixture of MPFPE, a fluorinated ether-based solvent that has lithium salt non-dissociation properties but is flame retardant, and DME, an ether-based solvent that has lithium salt dissociation properties. I was able to confirm.

<Experiment 3> Ion conductivity and flame retardant properties experiment according to the mixing ratio of the first and second solvents

In order to determine the ionic conductivity and flame retardant properties according to the mixing ratio of the first solvent and the second solvent, the mixing ratio of the first solvent and the second solvent was changed as shown in Table 3 below, and the ionic conductivity and flame retardant properties of the electrolyte solution were changed accordingly. was measured, and the results are shown in Table 3.

At this time, MPFPE was used as the first solvent, and DME was used as the second solvent.

And the flame retardant properties were conducted based on the flame retardancy test in <Experiment 1>.

division lithium salt First solvent (v/v)
(MPFPE) Second solvent (v/v)
(DME) Ion conductivity
(mS/cm Flame retardant
(sec/g) No. 7 2.0M LiTFSI 30 70 6.26 53 No. 8 2.0M LiTFSI 40 60 5.71 42 No. 9 2.0M LiTFSI 50 50 5.25 35 No. 10 2.0M LiTFSI 60 40 4.98 21

As can be seen in Table 3, No. 1 in which MPFPE, the first solvent, is mixed in a ratio of 50% or more. 9 and no. Case 10 is No. 1 in which MPFPE, the first solvent, is mixed in a ratio of less than 50%. 7 and no. It was confirmed that flame retardancy was significantly improved compared to case 8.

In particular, No. 1, where the mixing ratio of the first solvent and the second solvent is 6:4. In the case of 10, it was confirmed that the flame retardancy was the best.

However, in terms of ionic conductivity, it was confirmed that it gradually decreased as the mixing ratio of MPFPE, the first solvent, increased. However, in terms of ionic conductivity, even if the mixing ratio of MPFPE, the first solvent, increases, No. 1 where MPFPE, the first solvent, is mixed in a ratio of less than 50%. 7 and no. No. 8, in which the first solvent, MPFPE, is mixed in a ratio of 50% or more. 9 and no. In case 10, it was confirmed that the degree of decrease in ionic conductivity was low.

Therefore, in order to improve flame retardancy and maintain excellent ionic conductivity, it was confirmed that it is preferable to mix the first solvent and the second solvent so that the first solvent is 50% or more by weight.

<Experiment 4> Ion conductivity and discharge capacity experiment according to lithium salt concentration

With the mixing ratio of the first solvent and the second solvent fixed at 6:4, the concentration of lithium salt was changed as shown in Table 4 below, and the ionic conductivity of the electrolyte solution and the 1st chemical conversion process of the lithium secondary battery using the electrolyte solution were changed. Discharge characteristics were measured, and the results are shown in Table 4.

At this time, MPFPE was used as the first solvent, and DME was used as the second solvent.

division lithium salt
(LiTFSI) First solvent (v/v)
(MPFPE) Second solvent (v/v)
(DME) Ion conductivity
(mS/cm chemical process
1st discharge capacity
(mAh/g) No. 11 1.0M 60 40 6.28 187.7 No. 12 1.5M 60 40 5.82 188.8 No. 13 2.0M 60 40 4.98 194.7 No. 14 2.5M 60 40 2.55 187.4

As can be seen in Table 4, as the concentration of lithium salt increases, the ionic conductivity gradually decreases, but the 1st discharge capacity of the chemical process gradually increases as the concentration of lithium salt increases, and then decreases again to a high point of 2.0M.

Therefore, considering ionic conductivity and discharge capacity, it was confirmed that it is good to maintain the concentration of lithium salt at 1.0 to 2.0, preferably 2.0 mol. However, in this embodiment, since it is important to secure flame retardancy depending on the type of solvent, the concentration of lithium salt may be maintained in the range of 0.1 to 3.0 mol.

<Experiment 5> Discharge capacity and lifespan characteristics experiment according to the type of lithium salt

The types of the first solvent and the second solvent were changed as shown in Table 5 below, and the discharge capacity and life characteristics of the lithium secondary battery using the corresponding electrolyte were measured, and the results are shown in Table 5 and Figure 3.

Figure 3 is a graph showing the results of an experiment evaluating the discharge capacity and life capacity maintenance rate of Examples and Comparative Examples according to changes in the type of solvent.

division Comparative example Example (No. 13) lithium salt LiTFSI 1.0M 2.0M

menstruum EC 50 - EMC 50 - DME - 40 MPFPE - 60 Chemical process @0.1C 1st discharge capacity
(mAh/g) 187.7 194.7 Life characteristics @0.5C 1st discharge capacity
(mAh/g) 191.2 196.4 Life characteristics @0.5C 100th discharge capacity
(mAh/g) 161.7 174.8 Life characteristics (%) 84.6 89.0

As can be seen in Table 5 and Figure 3, compared to the comparative example using an electrolyte mixed at EC:EMC=1:1, which is used as an electrolyte for a conventional lithium secondary battery, No. 1 according to the embodiment of the present invention. In Example 13 where the electrolyte solution was applied, it was confirmed that both discharge capacity and lifespan characteristics were improved.

<Experiment 6> Discharge capacity experiment according to the type of lithium salt

The types of the first solvent and the second solvent were changed as shown in Table 5 below, and the discharge capacity and life characteristics of the lithium secondary battery using the corresponding electrolyte were measured, and the results are shown in Table 6 and Figure 4.

Figure 4 is a graph showing the results of an experiment evaluating the output performance of Examples and Comparative Examples according to changes in the type of solvent.

division Comparative example Example (No. 13) lithium salt LiTFSI 1.0M 2.0M

menstruum EC 50 - EMC 50 - DME - 40 MPFPE - 60 0.1C discharge capacity (mAh/g) 198 207 0.33C discharge capacity (mAh/g) 191 195 0.5C discharge capacity (mAh/g) 185 191 1.0C discharge capacity (mAh/g) 175 184 2.0C discharge capacity (mAh/g) 163 171 0.1C discharge capacity (mAh/g) 200 202

As can be seen in Table 6 and Figure 4, compared to the comparative example using an electrolyte mixed at EC:EMC=1:1, which is used as an electrolyte for a conventional lithium secondary battery, No. 1 according to the embodiment of the present invention. In Example 13 where the electrolyte solution was applied, it was confirmed that the discharge capacity was improved under all conditions.

Therefore, as can be seen from the above experiments, a first solvent consisting of a fluorinated ether-based solvent having flame retardant properties suggested in the present invention as a solvent for forming an electrolyte solution, and a second solvent consisting of an ether-based solvent having lithium salt dissociation properties 2 It was confirmed that when the solvent was mixed in an appropriate ratio, the flame retardancy, output characteristics, and lifespan characteristics of the lithium secondary battery were improved compared to when a conventional solvent was used.

In particular, it can be confirmed that in order to improve all flame retardancy, output characteristics and life characteristics, it is better to mix the first solvent and the second solvent according to the present invention at a ratio of 10:90 to 80:20, preferably 60:40. there was.

In addition, 1-methoxyheptafluoropropane (MPFPE), a fluorinated ether-based solvent with excellent flame retardant properties among fluorinated ether-based solvents, is used as the first solvent, and the second solvent is an ether-based solvent with excellent dissociation characteristics of lithium salts among ether-based solvents. It was confirmed that it is better to apply dimethyl ether (DME).

Although the present invention has been described with reference to the accompanying drawings and the above-described preferred embodiments, the present invention is not limited thereto and is limited by the claims described below. Accordingly, those skilled in the art can make various changes and modifications to the present invention without departing from the technical spirit of the claims described later.

Claims (9)

Lithium salt;
a first solvent consisting of a fluorinated ether-based solvent having lithium salt non-dissociation properties;
An electrolyte solution for a lithium secondary battery comprising a second solvent consisting of an ether-based solvent having lithium salt dissociation properties.
In claim 1,
The first solvent is an electrolyte solution for a lithium secondary battery, characterized in that it contains a fluorinated ether-based solvent, which is 1-methoxyheptafluoropropane, represented by [Formula 1] below.
… … … [Equation 1] In claim 1,
The second solvent is an electrolyte solution for a lithium secondary battery, characterized in that it contains dimethyl ether (DME).
In claim 1,
An electrolyte solution for a lithium secondary battery, characterized in that the mixing ratio of the first solvent and the second solvent is 50% or more of the first solvent by weight.
In claim 4,
An electrolyte solution for a lithium secondary battery, characterized in that the mixing ratio of the first solvent and the second solvent is 10:90 to 80:20 in weight ratio.
In claim 1,
An electrolyte solution for a lithium secondary battery, characterized in that the concentration of the lithium salt is 0.1 to 3.0 mol.
In claim 1,
The lithium salt is LiPF ₆ , LiBF ₄ , LiClO ₄ , LiCl, LiBr, LiI, LiB ₁₀ Cl ₁₀ , LiCF ₃ SO ₃ , LiCF ₃ CO ₂ , LiAsF ₆ , LiSbF ₆ , LiAlCl ₄ , CH ₃ SO ₃ Li, CF ₃ SO ₃ Li, LiN(SO ₂ C ₂ F ₅ ) ₂ , Li(CF ₃ SO ₂ ) ₂ N, LiC ₄ F ₉ SO ₃ , LiB(C ₆ H ₅ ) ₄ , LiB(C ₂ O ₄ ) ₂ , LiPO ₂ F ₂ , Li(SO ₂ F) ₂ N, LiFSI, or (CF ₃ SO ₂ ) ₂ NLi. An electrolyte solution for a lithium secondary battery, characterized in that one or two or more types are mixed.
A lithium secondary battery containing the electrolyte of claim 1.
In claim 8,
A positive electrode containing a positive electrode active material consisting of Ni, Co, and Mn;
A negative electrode containing one or two or more types of negative electrode active materials selected from carbon (C)-based or silicon (Si)-based;
A lithium secondary battery further comprising a separator interposed between the positive electrode and the negative electrode.